The invention relates to a device for measuring and calculating geometrical parameters or an object.
Such a device and such a process are known from EP 0 403 908. The known device comprises a basic body with a table on which a supporting apparatus for an object is displaceable. Above the table there is arranged a tripod structure which consists of three legs attached to the edge of the table, which are supplemented upwardly into a T-like portal. The three legs are mutually displaced by 90.degree.. Cameras are arranged or the legs which are movable on tracks in the vertical direction. A further stationary camera is situated in the centre of the T-like portal. The three cameras which are arranged on the legs as well as the camera which is arranged in the portal are directed towards the longitudinal central axis of the table. Illuminating devices are directly arranged on the respective cameras, which are directed towards the object to be measured.
The cameras are connected to an image Processing system. The profiles of the object to be measured are recorded simultaneously under several different angles of view. The measured profiles are compared with set profiles and displayed as curve diagrams or tables.
The cameras are exclusively arranged as incident light cameras, so that the supporting apparatus has to be moved for the measurement of various measuring points of the object in such a way that the measuring point is formed sharply in the cameras. The acquisition of the measured values is complicated and requires continuous control by the operating staff, because in the case of unfocused imaging the magnitude relationship of the reproduced points with the original would be erroneous and would lead to measuring errors.
The invention is thus based on the object or improving the aforementioned device in such a way that the measuring points can be accessed in a purposeful way, thus rendering the performance of the measurement simpler, faster and preciser.
This object is achieved in a device pursuant to the present invention.
In a first optical area measuring sensor, which is arranged as a transmitted light measuring sensor, the profile outline of the object to be measured is reproduced as a shadow image. As the image plane of the shadow of the profile outline is independent of the diameter of the object to be measured, the necessity concerning a separate adjustment of the distance between the object to be measured and the transmitted light measuring sensor for the focussing can be omitted. The imaging relationship of the shadow image of the object on the transmitted light measurement sensor is always constant, so that a determined measuring point on the outer profile of the object to be measured can be accessed by a second area measuring sensor arranged as an incident light measuring sensor in such a purposeful manner that this point is reproduced in the calibration plane and thus in the correct imaging scale on the incident light measuring sensor. A check concerning the sharpness by the operating staff is thus not required.
If the incident light measuring sensor id situated on a second slide which is jointly movable with the slide on which the transmitted light measuring sensor is arranged, then a selected measuring point can be accessed, for example, by driving the first slide with the transmitted light measuring sensor in such a way that it coincides with a marking which is identical with the calibration plane of the incident light measuring sensor. On reaching the point on the outer profile, the incident light measuring sensor is precisely situated in the position in which the same point is reproduced sharply. The imaging relationship of several points situated in the same plane is thus correct.
Preferably, the first slide is exclusively movable in one axial direction relative to the basic body and the supporting apparatus is arranged on a third slide which is movable relative to the basic body in the direction of the axis of rotation.
By limiting the degrees of freedom by which the first slide on the one hand and the third slide on the other hand are movable, there is a direct relationship of the paths of travel to the basic body, so that the adjustment faults which cannot be fully excluded in practice only enter the measuring results directly, but do not multiply, as would be the case in the overlapping of movements in several degrees of freedom. The overall measuring precision is thus improved over the known device.
To detect a measuring point from a third perspective it is possible to arrange on the second slide a third area measuring sensor which is arranged as an incident light measuring sensor, whose optical axis is aligned perpendicularly to the optical axes of the other area measuring sensors, or a pentaprism can optionally be inserted in the path of the rays of the incident light measuring sensor, through which the measuring axis of the incident light measuring sensor is deflectable at a right angle to its optical axis and the optical axis of the transmitted light measuring sensor.
Although the first alternative requires a higher technical complexity owing to the presence of a third area measuring sensor, it nevertheless offers the advantage that the image reproduction of a measuring point can occur simultaneously under three directions of observation. In the second alternative the pentaprism has to be inserted into the path of the rays in order to change the directions or observation of the incident light sensor. The two directions of observation can occur, however, through one and the same incident light measuring sensor. In addition to saving a third area measuring sensor, this solution also avoids the otherwise required holding means for the further area measuring sensor, so that a reduction in weight can thus be gained and the bearing and the drive for the second slide can be arranged more simply. This also reduces the stress on the first slide and its drive. By using a pentaprism it is ensured that the direction of observation of the incident light sensor is deflected precisely at a right angle and the precision of the alignment of the pentaprism does not enter the measuring result as a measuring error.
An illuminating device allocated to the transmitted light measuring sensor is preferably arranged coaxially to the optical axis of the transmitted light measuring sensor on the first slide on the side of the rotational axis of the light measuring sensor and comprises a collimator optical system which emits a parallel luminous pencil. The transmitted light measuring sensor comprises a telecentric optical system. This arrangement ensures that an object projects in any position of the path of the rays between the illuminating device and the transmitted light measuring sensor a shadow image with a sharp profile on the transmitted light measuring sensor with a constant imaging scale. This enables precise measurements of the outer profile for each size and position of an object to be measured without having to take any adjustment measures.
The illuminating device allocated to the incident light measuring sensor is arranged as an annular light which is arranged coaxially to the optical axis of the incident light measuring sensor. This arrangement of the illuminating device provides a very even illumination of the surface of the object to be measured. This ensues that leaps in the brightness only occur at the edges and corners of the imaged object, but not from an uneven illumination.
The optical system of the incident light measuring sensor is preferably adjusted in such a way that the optical axis of the transmitted light measuring sensor is situated in the calibration plane of the incident light measuring sensor. The two surface measuring sensors are a mutually coupled by this measure, whereby on displacing the transmitted light measuring sensor to a selected measuring point the same measuring point is automatically reproduced sharply on the incident light measuring sensor in another direction of observation which is rotated by 90.degree..
pursuant to a further development, a light barrier with a parallel small-calibre light pencil is arranged on the first slide parallel and adjacent to the transmitted light measuring sensor as well as on the level of its optical axis, and a sensor of the light barrier is connected with the computer. With this light barrier it is possible to carry out automatically an initial positioning of the axis. On crossing the light barrier, the free end of the object to be measured is then reproduced automatically in the centre of the transmitted light measuring sensor. If the object to be measured concerns a processing tool for example in which the measuring points to be accessed for determining the geometric parameters are situated in the vicinity of the free end of the object, then these areas are simultaneously reproduced on the transmitted light measuring sensor and can be accessed in a purposeful manner over the shortest possible path.
A least one distance sensor, which is connected to the computer, can be arranged next to the incident light measuring sensor and on the level of its optical axis. The surface profile can be scanned with this distance sensor by rotating the object, so that at first a rough alignment of the rotating position is possible through the determination of the distance minima and maxima or maxima of the distance gradients, which can then be corrected following the changeover to the transmitted light measuring sensor and the incident light measuring sensor.
Preferably, the distance sensor is arranged as an optical sensor, e.g. as a laser triangulator or as a mechanical scanner. A very fast contactless acquisition of measured values is possible with the laser triangulator. The mechanical scanner is favourably used in cases where a contactless optical measurement would supply imprecise results owing to the surface structure of the object to be measured or is not accessible to an optical measurement in cases of areas disposed in the inside of the object.
In a practical embodiment the path of movement of the slide towards the object is limited by a safety distance from the object. This excludes collisions by improperly clamped bodies or by faulty operations during the movement of the slides.
Concerning the process for measuring and calculating geometrical parameters, the invention is based on the object of improving a method pursuant to the preamble of claim 12 in the respect that optionally all relevant geometrical parameters of an object to be measured can be determined with as few measuring steps as possible and with high precision.
this object is achieved with a method pursuant to the present invention.
The object is positioned at first in its axial and rotational position in such a way that the relevant measuring points are in the imaging zone of the area measuring sensors or are in their ultimate vicinity, so that the measuring points can be accessed in a purposeful manner over short paths of movement. Depending on the type of the geometrical parameters to be measured and calculated, one or several process steps are carried out thereafter in order to place the measuring points or to calculate their coordinates. The desired geometrical parameters of the object can then be calculated according to mathematical functions from individual measuring points of ones that are linked into groups. Several alternatives are possible for the evaluation of the geometrical parameters. The geometrical parameters can either be displayed or stored in order to obtain the characteristic parameters for an object. Furthermore, it is possible that the parameters are compared with an article database in order to separate defective products through quality control or to evaluate and sort them according to quality classes. In addition, there is also the possibility to provide follow-up control to a production machine on the basis of a statistical evaluation of the geometrical parameters so as to take influence on the quality already during production and to reduce the rejection rate of defective items.
To enable the measurement of coordinates of measuring points of the object which are disposed in lower regions than the outer profile of the object and thus cannot be reproduced on the transmitted light measuring sensor, it is provided that the coordinates are determined by moving the incident light measuring sensor from an initial position to a position in which the measuring point is reproduced sharply on the incident light measuring sensor and by measuring the path of movement. As an alternative this can also occur by contactless distance measurement with an optical distance sensor, e.g. a laser triangulator, or by moving a scanner up to the point of contact with the measuring point when a contactless optical measurement of the inner profile of a hollow object, for example, is not possible. A surface profile of such interior areas can also be obtained from a plurality of such coordinates gained.
The incident light measuring sensor is moved depending on the position of the transmitted light measuring sensor, with the incident light measuring sensor being focused on the optical axis of the transmitted light measuring sensor. This mandatorily results in a coupling of the two area measuring sensors, so that by accessing a point on the surface profile of the object by the transmitted light measuring sensor this point is automatically reproduced sharply on the incident light measuring sensor. Measuring points which are situated in the same imaging plane as the incident light measuring sensor can be measured by the incident light measuring sensor without any further displacing movements.
An initial axial positioning of the object can be carried out in such a way that the object and the transmitted light measuring sensor are moved relative to one another so far in the direction of the rotational axis until the maximum of the outer profile of the object extending in the direction of the rotational axis crosses the beam of a light barrier arranged on the level of the optical axis of the transmitted light measuring sensor. During this rough positioning the relevant measuring points are located in measuring sensor and can be accessed in a purposeful manner. This type of initial axial positioning is possible with fast speeds of travel and automatically, so that the total time required to access the individual measuring points can be reduced.
An initial rotational positioning of the object can be carried out in such a way that the object is turned and that a continuous measurement of the distance between the surface of the object and the distance sensor is carried out by means of the distance sensor and the object is finally placed in a rotational position in which one of the distance minima or the distance gradient maxima is in a predetermined rotational position towards the optical axis of the transmitted light measuring sensor. This process can also be carried out automatically at a high rotational speed, which contributes in reducing the entirely required time for accessing the measuring points.
A further increase in the precision can be obtained when a potential inclined position of the object is determined by forming the difference between different diameter or distance extreme values in at least one plane and a wobble cone is calculated from the difference of the diameter and distance extreme values, with the calculated coordinates being corrected by the distance of the envelope surface of the cone from the rotational axis. It is possible by such a correction to eliminate errors which may occur as a result of wear and tear, soiling or other faults in the supporting apparatus or during its operation.
several alternatives can be used in determining the measuring points. The measuring points can be predetermined manually for example in order to measure an object individually. Furthermore, search areas of the measuring points can be predetermined manually in a first step. In a second step the corners and/or edges of the object situated in these search areas are determined automatically in that the position of the corners and/or edges is determined by an image processing program from the evaluation of the changes in at least one characteristic of the image reproduction of the object on the area measuring sensors, such as changes in the course of the brightness or texture or colour of the image reproduction of the object on the area measuring sensors.
This measure only requires roughly accessing the measuring points and is thus faster than the aforementioned variant and, concerning its precision, is independent of the precision with which the operator accesses the measuring points.
It is furthermore possible to have search areas of the measuring points calculated in a first step by entering parameters for groups of bodies to be measured, to automatically predetermine the search areas in a second step and to automatically determine in a third step the corners and/or edges of the object situated if these search areas in such a way that the position of the corners and/or edges is determiner by an image processing program from the evaluation of the changes in at least one characteristic of the image reproduction of the object on the area measuring sensors, such as changes in the course of the brightness or texture or colour of the image reproduction of the object on the area measuring sensors.
This alternative places low requirements of the instructions for the operating staff and allows the automatic quality control of products. As the measuring points to be accessed need not be determined manually, this alternative allows a particularly fast determination of the desired geometrical parameters.
According to a third alternative, the measuring points can be determiner automatically by scanning a plurality of points on corners and/or edges of the object, with the position of the corners and/or edges being determined by an image processing program from the evaluation of the changes in at least one characteristic of the image reproduction of the object on the area measuring sensors, such as changes in the course of the brightness or texture or colour of the image reproduction of the object on the area measuring sensors. This measure allows a fully automatic determination of the geometrical parameters of bodied. As contrary to the aforementioned alternatives it is necessary in this case to access several measuring points, a higher measuring time must be expected here.
Pursuant to a further development, the geometrical parameters of a subject processed with the processing tool can be calculated from the geometrical parameters of an object arranged as a processing tool.
This measure allows, for example, on the basis of predetermined tolerances to determine the tolerances of a processing tool with which the subject can be produced under adherence to the predetermined tolerances.
It is further possible to calculate from the geometrical parameters of an object arranged as a subject the geometrical parameters of a processing tool which is used for its production.
In this way it is possible to obtain construction data for the construction of a suitable tool.